Field of the Invention--This invention concerns fibrous batts of thermal insulation and more particularly concerns a method and apparatus for producing a smooth, tough elastomeric coating over one surface of a fibrous batt.
Description of the Prior Art--Fibrous batts of glass fibers are employed as thermal insulation and acoustical insulation in a variety of products, for example, ventilation duct-liners, automotive hood lid liners, et cetera. Tough, elastomeric coatings are applied to the exposed surface of such fibrous batts in order to retard separation of fibers and to reduce air friction losses in ducts which are lined with such batts. The coatings also increase the ease of handling the batts.
Typically such batts are coated on one surface with an elastomeric aqueous cross-linkable emulsion composition such as an acrylic emulsion which is heat cured after application. Such elastomeric cross-linkable compositions have been frothed or foamed in order to provide uniform coating of the exposed surface of the batt over the irregular and uneven surface of the batt. During thermal exposure such emulsion coating compositions lose water and the frothed or foamed coatings collapse (i.e., coalesce and eliminate bubbles from the froth or foam). Continuous thermal exposure cross-links the elastomeric resins to a tough coating which provides an economical, thin exposed coating which generally conforms to the irregularities of the initial fibrous batt. The resulting relatively rough and uneven surface is objectionable in ventilation duct liners for several reasons. Airborne dust and particles tend to accumulate in the surface irregularities. Viri, bacteria and pathogens tend to accumulate in the irregularities of the surface. Irregular surfaces increase the frictional resistance of air moving through the lined ducts. Smoother surfaces tend to reduce the frictional resistance of the lined ducts to the flow of air.
Cross-linkable aqueous emulsions are available from several sources. A cross-linkable emulsion contains monomers and polymers, some of which have multiple polymerizable sites to effect cross-linking to a three-dimensional polymer. Aqueous acrylic emulsions are preferred. Any cross-linkable aqueous acrylic emulsion which is not a pressure-sensitive adhesive is acceptable.